<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<select id="sltCity">
    <option value="1">北京</option>
    <option value="2">天津</option>
    <option value="3">成都</option>
</select>
</body>
<script>

   var sltCity = document.getElementById('sltCity');
   sltCity.onchange = cityChange;

   function cityChange () {

     var opt=  this.selectedOptions[0];
     alert(opt.value);
     alert(opt.text);

   }
</script>
</html>